Question

A) When the tube is filled with mercury vapor, as in this case, a
sharp drop in the collected current is observed when the
accelerating potential reaches 4.9 . The current drops suddenly to
a negligible value and slowly increases again when the accelerating
potential is above 4.9 . What is the energy absorbed by the atomic
electrons in the mercury atom when the accelerating potential is
4.9 ?
B) The excited mercury atoms decay back to the lowest energy level
by emitting radiation. What is the wavelength of this radiation?